Integrated production of FCC-produced C2 and ethyl benzene

ABSTRACT

Processing schemes and arrangements are provided for obtaining ethylene and ethane via the catalytic cracking of a heavy hydrocarbon feedstock and converting the ethylene into ethyl benzene without separating the ethane from the feed stream. The disclosed processing schemes and arrangements advantageously eliminate any separation of ethylene from ethane produced by a FCC process prior to using the combined ethylene/ethane stream as a feed for an ethyl benzene process. Further, heat from the alkylation reactor is used for one of the strippers of the FCC process and at least one bottoms stream from alkylation process is used as an absorption solvent in the FCC process.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Division of prior copending U.S. application Ser.No. 11/924,809 which was filed Oct. 26, 2007, the contents of which areincorporated herein by reference thereto.

TECHNICAL FIELD

This disclosure relates generally to hydrocarbon processing. Morespecifically, this disclosure relates to the initial processing ofhydrocarbon-containing materials into an intermediate stream of ethaneand ethylene, produced by the cracking of a heavy hydrocarbon feedstock.This disclosure also relates to the subsequent use of said intermediatestream in the making of valuable aromatics, such as ethyl benzene.

BACKGROUND OF THE RELATED ART

Light olefins serve as feed materials for the production of numerouschemicals. Light olefins have traditionally been produced through theprocesses of steam or catalytic cracking of hydrocarbons derived frompetroleum sources. Fluidized catalytic cracking (FCC) of heavyhydrocarbon streams is commonly carried out by contacting relativelyhigh boiling hydrocarbons with a catalyst composed of finely divided orparticulate solid material. The catalyst is transported in a fluid-likemanner by transmitting a gas or vapor through the catalyst at sufficientvelocity to produce a desired regime of fluid transport. Contact of theoil with the fluidized catalyst results in the cracking reaction.

FCC processing is more fully described in U.S. Pat. Nos. 5,360,533,5,584,985, 5,858,206 and 6,843,906. Specific details of the variouscontact zones, regeneration zones, and stripping zones along witharrangements for conveying the catalyst between the various zones arewell known to those skilled in the art.

The FCC reactor serves to crack gas oil or heavier feeds into a broadrange of products. Cracked vapors from an FCC unit enter a separationzone, typically in the form of a main column, that provides a gasstream, a gasoline cut, light cycle oil (LCO) and clarified oil (CO)which includes heavy cycle oil (HCO) components. The gas stream mayinclude hydrogen and C₁ and C₂ hydrocarbons, and liquefied petroleum gas(“LPG”), i.e., C₃ and C₄ hydrocarbons.

There is an increasing need for light olefins such as ethylene for theproduction of polyethylene, ethyl benzene and the like as opposed toheavier olefins. Research efforts have led to the development of an FCCprocess that produces or results in greater relative yields of lightolefins, e.g., ethylene. Such processing is more fully described in U.S.Pat. No. 6,538,169.

Ethyl benzene is an important intermediate compound for the productionof styrene. Although often present in small amounts in crude oil, ethylbenzene is produced in bulk quantities by combining the petrochemicalsbenzene and ethylene in an acid or zeolite catalyzed chemical reaction.Catalytic dehydrogenation of the ethyl benzene then gives hydrogen gasand styrene.

A conventional FCC process produces a combined ethylene/ethane stream.The ethylene/ethane stream is typically run through a splitter ordistillation column to separate the ethylene from the ethane. Theoperation of such a splitter is energy intensive in addition toconstruction and maintenance costs.

In view of the increasing need and demand for light olefins such asethylene and the use thereof in producing ethyl benzene, there is a needand a demand for improved processing and arrangements for the separationand recovery of light olefins, such as ethylene, from such FCC processeffluent and the efficient conversion of those olefins into usefularomatic intermediates, such as ethyl benzene.

SUMMARY OF THE INVENTION

An integrated process is disclosed for (i) catalytically cracking (FCC)a heavy hydrocarbon feedstock, (ii) obtaining a combined ethylene/ethanestream, and (iii) reacting the ethylene of the combined ethane/ethylenestream with benzene to produce an ethyl benzene product stream. Theintegrated process comprises contacting a heavy hydrocarbon feedstockwith a hydrocarbon cracking catalyst in a fluidized reaction zone toproduce a hydrocarbon effluent stream that includes ethane and ethylene.The process then further comprises separating the combinedethane/ethylene stream from the hydrocarbon effluent stream, passing thecombined ethane/ethylene stream to an alkylation reactor, and reactingat least some of the ethylene of the combined ethane/ethylene streamwith benzene in the alkylation reactor to produce ethyl benzene.

By linking the FCC process directly to the ethyl benzene alkylationprocess, substantial capital and energy costs savings are achieved.First, the need for an ethylene/ethane splitter column is eliminated asethane is inert to the ethyl benzene alkylation process and does nothinder the process in an appreciable way. Second, along with the energysavings achieved by eliminating the ethylene/ethane splitter, additionalenergy savings are achieved by linking the intercoolers used to cool thealkylation reactor to one of the splitter columns of the FCC process.Further, additional savings may achieved by using the bottoms streamfrom the ethyl benzene column of the alkylation zone in one of two ways.First the EB column bottoms may be used as a solvent in the primaryabsorber of the absorption zone, thereby reducing the dependence upondebutanized gasoline recycle as a solvent for the primary absorber.Second, the EB column bottoms may be used as a co-feed with the effluentstream to the main column of the separation zone. Employing either ofthese strategies can reduce the debutanized gasoline recycle demand by 5to 10%.

The ethane is preferably not stripped from the combined ethane/ethylenestream prior to the combined ethane/ethylene stream entering thealkylation reactor. The ethane content of the combined ethane/ethylenestream may be up to or about 30 wt %.

Further, the combined ethane/ethylene stream entering the alkylationreactor is cold as it preferably has just passed through a demethanizer.The combined ethane/ethylene stream has a temperature of less than 0° C.(32° F.) which further reduces the duty of the intercoolers used to coolthe alkylation reactor.

The alkylation reactor preferably includes six catalyst beds, six feedinlets, and two intercoolers disposed between the second and fourthcatalyst beds.

As noted above, the hydrocarbon effluent generated in the FCC processpasses through a separation zone to form a separator liquid stream and aseparator vapor stream. C₂− hydrocarbon materials are stripped from theseparator liquid stream in a stripper column to form a C₃+ hydrocarbonprocess stream substantially free of C₂− hydrocarbons. This strippercolumn may be advantageously heated with heat generated in thealkylation reactor. Thus, heat may be transferred from the intercoolersused to cool the alkylation reactor to the stripper column to lessen thecooling duty of the intercoolers.

Further, in generating the ethane/ethylene combined stream, theseparator vapor stream is contacted with an absorption solvent in anabsorption zone to remove C₃+ hydrocarbons therefrom to form thecombined ethane/ethylene stream. More specifically, the separator vaporstream is contacted with the first absorption solvent comprisingdebutanized gasoline recycle in a primary absorber to form a firstprimary absorber process stream comprising ethane and ethylene andresidual amounts of C₃+ hydrocarbons. In one embodiment, the firstabsorption solvent used in the primary absorber also comprises a bottomsstream from an ethyl benzene (EB) column of the ethyl benzene process.Employing this option eliminates the need for a transalkylation sectionas well as a polyethyl benzenes (PEB) column in the alkylation process.The EB bottoms stream supplements some of the debutanized gasolinerecycle that is also used as the solvent in the primary absorber,thereby reducing the amount of recycle that is required. Any diethylbenzene (DEB) and polyethyl benzene (PEB) would ultimately end up as ahigh octane component in the gasoline product of the FCC process.

Another alternative is to send the EB column bottoms to the FCC mainseparation zone column, where the heavier species would be removed in aheavier fraction such as the heavy naphtha draw. The lighter species inthis stream would still act to reduce the required debutanized gasolinerecycle for use as the primary absorber solvent and will exit in theunstabilized gasoline that is recovered from the main column overhead.

Treatments to remove carbon dioxide, hydrogen sulfide, acetylene andmethane from the combined ethane/ethylene stream may be carried outprior to passing of the ethane/ethylene stream to the alkylationreactor.

An integrated system for (i) catalytically cracking a hydrocarbonfeedstock, (ii) obtaining selected hydrocarbon fractions including acombined ethane/ethylene stream and (iii) reacting the ethylene of thecombined ethane/ethylene stream with benzene to produce an ethyl benzeneproduct stream is provided. The integrated system includes a fluidizedreactor zone wherein the hydrocarbon feedstock contacts a catalyst toproduce a cracked effluent stream including ethane and ethylene. Thesystem also includes a separation zone for separating the crackedeffluent stream into at least one separator liquid stream and aseparator vapor stream. The at least one separator liquid streamincludes C₃+ hydrocarbons; the separator vapor stream includes ethaneand ethylene. The system also includes an absorption zone to absorb C₃+hydrocarbons from the separator vapor stream to form an absorption zoneeffluent stream comprising ethane and ethylene and a treatment zone toremove impurities other than ethane and ethylene from the absorptionzone effluent stream to provide a combined ethane/ethylene stream. Thecombined ethane/ethylene stream is fed through a process line to analkylation reactor for reacting at least some of the ethylene in thecombined ethane/ethylene stream with benzene to form ethyl benzene.

Intercoolers used to cool the alkylation reactor can be used to driveone or more reboilers of a splitter column. The bottoms stream from anethyl benzene column can be used as an absorber solvent or can be addedto the cracked effluent stream.

Other advantages will be apparent to those skilled in the art from thefollowing detailed description taken in conjunction with the appendedclaims and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified schematic diagram of a system for catalyticcracking a heavy hydrocarbon feedstock and obtaining selectedhydrocarbon fractions, including C2 light olefins via anabsorption-based product recovery;

FIG. 2 is a simplified schematic diagram of a system for convertingethylene and benzene to ethyl benzene that is integrated with the systemof FIG. 1; and

FIG. 3 is a simplified schematic diagram of another system forconverting ethylene and benzene to ethyl benzene that is also integratedwith the system of FIG. 1.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

FIG. 1 schematically illustrates a system 10 a for catalytic cracking aheavy hydrocarbon feedstock and obtaining light olefins viaabsorption-based product recovery and FIGS. 2 and 3 schematicallyillustrate systems 10 b, 10 c for efficiently converting the lightolefins from the system 10 a into one or more useful intermediates.Those skilled in the art and guided by the teachings herein providedwill recognize and appreciate that the illustrated systems 10 a, 10 b,10 c have been simplified by eliminating some usual or customary piecesof process equipment including some heat exchangers, process controlsystems, pumps, fractionation systems, and the like. It may also bediscerned that the process flows depicted in FIGS. 1-3 may be modifiedin many aspects without departing from the basic overall conceptsdisclosed herein.

In the cracking system 10 a, a suitable heavy hydrocarbon feedstockstream is introduced via a line 12 into a fluidized reactor zone 14wherein the heavy hydrocarbon feedstock contacts a hydrocarbon crackingcatalyst zone to produce a hydrocarbon effluent comprising a range ofhydrocarbon products, including light olefins such as ethylene and lighthydrocarbons such as ethane.

Suitable fluidized catalytic cracking reactor zones for use in thepractice of such an embodiment may, as is described in above-identifiedU.S. Pat. No. 6,538,169, include a separator vessel, a regenerator, ablending vessel, and a vertical riser that provides a pneumaticconveyance zone in which conversion takes place. The arrangementcirculates catalyst and contacts the catalyst with the feed.

More specifically and as described therein, the FCC catalyst typicallycomprises two components that may or may not be on the same matrix. Thetwo components are circulated throughout the reactor 14. The firstcomponent may include any of the well-known catalysts that are used inthe art of fluidized catalytic cracking, such as an active amorphousclay-type catalyst and/or a high activity, crystalline molecular sieve.Molecular sieve catalysts are preferred over amorphous catalysts becauseof their much-improved selectivity to desired products. Zeolites are themost commonly used molecular sieves in FCC processes. Preferably, thefirst catalyst component comprises a large pore zeolite, such as aY-type zeolite, an active alumina material, a binder material,comprising either silica or alumina and an inert filler such as kaolin.

The zeolitic molecular sieves appropriate for the first catalystcomponent should have a large average pore size. Typically, molecularsieves with a large pore size have pores with openings of greater than0.7 nm in effective diameter defined by greater than 10 and typically 12membered rings. Pore Size Indices of large pores are above about 31.Suitable large pore zeolite components include synthetic zeolites suchas X-type and Y-type zeolites, mordenite and faujasite. It has beenfound that Y zeolites with low rare earth content are preferred in thefirst catalyst component. Low rare earth content denotes less than orequal to about 1.0 wt % rare earth oxide on the zeolite portion of thecatalyst. Octacat™ catalyst made by W. R. Grace & Co. is a suitable lowrare earth Y-zeolite catalyst.

The second catalyst component comprises a catalyst containing, medium orsmaller pore zeolite catalyst exemplified by ZSM-5, ZSM-11, ZSM-12,ZSM-23, ZSM-35, ZSM-38, ZSM-48, and other similar materials. U.S. Pat.No. 3,702,886 describes ZSM-5. Other suitable medium or smaller porezeolites include ferrierite, erionite, and ST-5, developed by Petroleosde Venezuela, S. A. The second catalyst component preferably dispersesthe medium or smaller pore zeolite on a matrix comprising a bindermaterial such as silica or alumina and an inert filer material such askaolin. The second component may also comprise some other activematerial such as Beta zeolite. These catalyst compositions have acrystalline zeolite content of 10-25 wt % or more and a matrix materialcontent of 75-90 wt %. Catalysts containing 25 wt % crystalline zeolitematerial are preferred. Catalysts with greater crystalline zeolitecontent may be used, provided they have satisfactory attritionresistance. Medium and smaller pore zeolites are characterized by havingan effective pore opening diameter of less than or equal to 0.7 nm,rings of 10 or fewer members and a Pore Size Index of less than 31.

The total catalyst composition should contain 1-10 wt % of a medium tosmall pore zeolite with greater than or equal to 1.75 wt % beingpreferred. When the second catalyst component contains 25 wt %crystalline zeolite, the composition contains 4-40 wt % of the secondcatalyst component with a preferred content of greater than or equal to7 wt %. ZSM-5 and ST-5 type zeolites are particularly preferred sincetheir high coke resistivity will tend to preserve active cracking sitesas the catalyst composition makes multiple passes through the riser,thereby maintaining overall activity. The first catalyst component willcomprise the balance of the catalyst composition. The relativeproportions of the first and second components in the catalystcomposition will not substantially vary throughout the FCC unit 14.

The high concentration of the medium or smaller pore zeolite in thesecond component of the catalyst composition improves selectivity tolight olefins by further cracking the lighter naphtha range molecules.But at the same time, the resulting smaller concentration of the firstcatalyst component still exhibits sufficient activity to maintainconversion of the heavier feed molecules to a reasonably high level.

The relatively heavier feeds suitable for processing in accordanceherewith include conventional FCC feedstocks or higher boiling orresidual feeds. A common conventional feedstock is vacuum gas oil whichis typically a hydrocarbon material prepared by vacuum fractionation ofatmospheric residue and which has a broad boiling range of from 315-622°C. (600-1150° F.) and, more typically, which has a narrower boilingpoint range of from 343-551° C. (650-1025° F.). Heavy or residual feeds,i.e., hydrocarbon fractions boiling above 499° C. (930° F.), are alsosuitable. The fluidized catalytic cracking processing the invention istypically best suited for feedstocks that are heavier than naptha rangehydrocarbons boiling above about 177° C. (350° F.).

The effluent or at least a selected portion thereof is passed from thefluidized reactor zone 14 through a line 16 into a hydrocarbonseparation system 20, which may include a main column section 22 and astaged compression section 24. The main column section 22 may desirablyinclude a main column separator and associated overhead receiver wherethe fluidized reactor zone effluent can be separated into desiredfractions including a main column vapor stream that is passed throughline 26 to the two stage compressor 24, and a main column liquid stream,which is passed through line 30 to the absorber 40. To facilitateillustration and discussion, other fraction lines such as including aheavy gasoline stream, a light cycle oil (“LCO”) stream, a heavy cycleoil (“HCO”) stream and a clarified oil (“CO”) stream, for example, maynot be shown or specifically described.

The main column vapor stream line 26 is introduced into the stagedcompression section 24. The staged compression section 24 results in theformation of a high pressure separator liquid stream in a line 32 and ahigh pressure separator vapor stream in a line 34. While the pressure ofsuch high pressure liquid and high pressure vapor can vary, in practicesuch streams are typically at a pressure ranging from about 1375 kPag toabout 2100 kPag (about 200 psig to about 300 psig). The compressionsection 24 may also result in the formation of a stream of spill backmaterials largely composed of heavier hydrocarbon materials and such ascan be returned to the main column section 22 via the line 35.

The high pressure separator liquid stream 32 includes C₃+ hydrocarbonsand is substantially free of carbon dioxide and hydrogen sulfide. Thehigh pressure separator vapor stream 34 includes C₃− hydrocarbons andtypically includes some carbon dioxide and hydrogen sulfide.

The separator vapor stream line 34 is introduced into an absorption zone36, which includes the primary absorber 40, where the separator vaporstream 34 is contacted with a debutanized gasoline material provided bythe line 42 and the main column overhead liquid stream 30 to absorb C₃+materials and separate C₂ and lower boiling fractions from the separatorvapor stream. In general, the absorption zone 36 includes the primaryabsorber 40 that suitably includes a plurality of stages with at leastone and preferably two or more intercoolers interspaced therebetween toassist in achieving desired absorption. In practice, such a primaryabsorber 40 includes about five absorber stages between each pair ofintercoolers. The primary absorber 40 may include at least about 15 to25 ideal stages with 2 to 4 intercoolers appropriately spacedtherebetween.

C₃+ hydrocarbons absorbed in or by the debutanized gasoline stream 42and main column liquid stream 30 in the absorber 40 can be passed viathe line 43 back to the two-stage compressor 24 for further processing.The off gas from the primary absorber 40 passes via a line 44 to asecondary or sponge absorber 46. The secondary absorber 46 contacts theoff gas with light cycle oil from a line 50. Light cycle oil absorbsmost of the remaining C₄ and higher hydrocarbons and returns to the mainfractionators via a line 52. A stream of C₂− hydrocarbons is withdrawnas off gas from the secondary or sponge absorber 46 in the line 54 forfurther treatment as later described herein.

The high pressure liquid stream 32 from the compressor 24 is passedthrough to the stripper 62 which removes most of the C₂ and lightergases through the line 64 and passes them back to the compressor 24. Inpractice, the stripper 62 can be operated at a pressure ranging fromabout 1375 kPag to about 2100 kPag (about 200 psig to about 300 psig)with a C₂/C₃ molar ratio in the stripper bottoms of less than 0.001 andpreferably with a C₂/C₃ molar ratio in the stripper bottoms of less thanabout 0.0002 to about 0.0004.

As discussed in greater detail below, the reboiler heat exchanger 63 maybe heated by the alkylation reactor 164 shown in FIGS. 2 and 3.Specifically, one or more inter-coolers 63 a, 63 b (FIGS. 2-3) may becombined with the reboiler heat exchanger 63 (FIG. 1) associated withthe stripper 62.

As shown, the C₂ and lighter gases in the line 64 are combined in thecompressor 24 with the main column vapor stream 26 to form with highpressure separator vapor stream 34 that is fed into the primary absorber40. The stripper 62 supplies a liquid C₃+ stream 66 to the debutanizer70. A suitable debutanizer 70 includes a condenser (not shown) thatdesirably operates at a pressure ranging from about 965 kPag to about1105 kPag (about 140 psig to about 160 psig), with no more than about 5mol % C₅ hydrocarbons in the overhead and no more than about 5 mol % C₄hydrocarbons in the bottoms. More preferably, the relative amount of C₅hydrocarbons in the overhead is less than about 1-3 mol % and therelative amount of C₄ hydrocarbons in the bottoms is less than about 1-3mol %.

A stream of C₃ and C₄ hydrocarbons from the debutanizer 70 is taken asoverhead through the line 72 for further treatment as described belowand the bottoms stream 76 from the debutanizer 70 comprises gasoline,part of which forms the stream 42 which is fed to the top of the primaryabsorber 40 where it serves as the primary first absorption solvent.Another portion of the stream of debutanized gasoline is passed in theline 77 to a naphtha splitter (not shown), which may be a dividing wallseparation column.

The C₂− hydrocarbon stream 54 withdrawn from the secondary or spongeabsorber 46 is passed through a further compression section 90 to form acompressed vapor stream 92 that is passed into a compression ordischarge vessel 94. The discharge vessel 94 forms a liquid knockoutstream generally composed of heavy components (e.g., C₃+ hydrocarbonsthat liquefy in the discharge vessel 94) and are withdrawn in the line96. The discharge vessel 94 also forms an overhead vapor stream 100,primarily comprising C₂− hydrocarbons, with typically no more than traceamounts (e.g., less than 1 wt %) of C₃+ hydrocarbons.

The overhead stream 100 is passed to an amine treatment section 102 toremove CO₂ and H₂S. The utilization of amine treatment system 102 forcarbon dioxide and/or hydrogen sulfide removal is well known in the art.Conventional such amine treatment systems typically employ an aminesolvent such as methyl diethanol amine (MDEA) to absorb or otherwiseseparate CO₂ and H₂S from hydrocarbon stream materials. A stripper orregenerator is typically subsequently used to strip the absorbed CO₂ andH₂S from the amine solvent, permitting the reuse of the amine solvent.

While such amine treatment has proven generally effective for removal ofcarbon dioxide from various hydrocarbon-containing streams, theapplication of such amine treatment to ethylene-rich hydrocarbon andcarbon dioxide-containing streams, such as being processed at this pointof the subject system, may experience some undesired complications assome of the olefin material may be co-absorbed with the CO₂ and H₂S inor by the amine solvent. Such co-absorption of olefin materialundesirably reduces the amounts of light olefins available for recoveryfrom such processing. Moreover, during such subsequent stripperprocessing of the amine solvent, the presence of such olefin materialscan lead to polymerization. Such polymerization can lead to degradationof the amine solvent and require expensive off-site reclamationprocessing.

In view thereof, it may be desirable to utilize an amine treatmentsystem such as includes or incorporates a pre-stripper interposedbetween the amine system absorber and the amine systemstripper/regenerator. Such an interposed pre-stripper, can desirablyserve to separate hydrocarbon materials, including light olefins such asethylene, from the carbon dioxide and amine solvent prior to subsequentprocessing through the regenerator/stripper. A CO₂/H₂S outlet is shownat 103.

A stream 104 containing C₂− hydrocarbons substantially free of carbondioxide and hydrogen sulfide passes to a dryer section 106 with a wateroutlet line 107. A stream containing dried C₂− hydrocarbonssubstantially free of carbon dioxide and hydrogen sulfide passes via aline 108 to an acetylene conversion section or unit 110. As is known inthe art, acetylene conversion sections or units are effective to convertacetylene to form ethylene. Thus, an additionally ethylene-enrichedprocess stream 112 is withdrawn from the acetylene conversion section orunit 110 and passed to the optional dryer 114 or to the CO₂, carbonylsulfide (“COS”), arsine and/or phosphine treater 116 as is known in theart to effect removal of CO₂, COS, arsine and/or phosphine.

Water is withdrawn from the dryer 114 through the line 117. CO₂, COS,Arsine and/or Phosphine are withdrawn through the line 118, and thetreated stream 120 is introduced into a demethanizer 122. A suitabledemethanizer 122 may include a condenser (not specifically shown) thatdesirably operates at a temperature of no greater than about −90° C.(−130° F.), more preferably operates at a temperature ranging from about−90° C. to about −102° C., preferably about −96° C. (−130° to about−150° F., preferably at about −140° F.). In addition, the demethanizer122 may operate with a methane to ethylene molar ratio in the bottoms ofno greater than about 0.0005 and, more preferably at a methane toethylene molar ratio in the bottoms of no greater than about 0.0003 toabout 0.0002.

The overhead stream 124 of methane and hydrogen gas from thedemethanizer 122 may be used as a fuel or, if desired, taken for furtherprocessing or treatment such as to a pressure swing absorption unit (notshown) for H₂ recovery. The demethanizer outlet stream 126 is passeddirectly to an ethyl benzene unit 10 b of FIG. 2 or 10 c of FIG. 3without the need for heating or a splitter to separate the ethane fromthe ethylene. By avoiding the use of a C₂/C₂=splitter, which wouldoperate at a pressure ranging from about 1930 kPag to about 2105 kPag(about 280 psig to about 305 psig), substantial savings in terms ofoperating coast and capital costs are achieved.

Still referring to FIG. 1, the stream 72 containing C₃ and C₄hydrocarbons taken overhead from the debutanizer 70 may contain somesignificant relative amounts of hydrogen sulfide and is thereforepreferably passed to a hydrogen sulfide removal treatment unit 128, suchas an amine treatment section, where hydrogen sulfide is removed throughthe line 129 and the treated stream 130 is passed to an optionalextraction unit 132 to catalytically oxidize mercaptans present todisulfides via a caustic wash, which are removed through the line 134.

The resulting stream 136 is passed to the C₃/C₄ splitter 138. A suitableC₃/C₄ splitter includes a condenser (not specifically shown) thatdesirably operates at a pressure ranging from about 1650 kPag to about1800 kPag (about 240 psig to about 260 psig), preferably at a pressureof about 1724 kPa (about 250 psig) and desirably operates such thatthere is no more than about 5 mol % C₄s in the overhead product stream,preferably less than about 1 mol % C₄s in the overhead product streamand no more than about 5 mol % C₃s in the bottoms stream, preferablyless than about 1 mol % C₃s in the bottoms stream.

The C₃/C₄ splitter 138 forms a bottoms stream 140 of C₄+ hydrocarbonsfor use as either for product recovery or further desired processing, asis known in the art. The C₃/C₄ splitter 138 also forms a stream 142composed primarily of C₃ hydrocarbons which is passed to apropylene/propane splitter 144. A suitable such propane/propylenesplitter 144 may operate such that at least 98 wt % and, preferably, atleast about 99 wt % of the propylene is recovered in the overhead streamand the propylene in the overhead stream is at least about 99.5% pure.

The propylene/propane splitter 144 forms a propylene stream 146 and apropane stream 148. The propylene stream 146 may be passed to dryer 150for the removal of water through the line 152 before being passed on toa regenerative COS treater 154 to remove COS through the line 156 beforebeing passed through the arsine and/or phosphine treater 158 to effectremoval of trace amounts of arsine and/or phosphine through the line 160and producing an propylene product stream 162.

Turning to FIG. 2, the combined ethane/ethylene stream 126 is introducedat various stages 165 a-165 f of the alkylation reactor 164, withoutpre-heating and without separating the ethane, where the ethylene reactscatalytically with benzene provided in the form of fresh benzene throughthe line 166 and recycled benzene through the line 168. Because ethaneis essentially inert to the ethyl benzene process system 170, the needfor an upstream ethane/ethylene splitter is not required. Further,pre-heating the cool stream 126 from the demethanizer 122 is notrequired as the low temperatures have been surprisingly found to improveselectivity in the alkylation reactor 164 as explained below. As thematerial in the combined ethane/ethylene stream 126 is liquid, it may bedelivered at pressures ranging from about 2900 to about 4000 kPa (˜421to ˜580 psi) using a conventional pump 125 instead of a more expensivecompressor that would be required to deliver polymer grade ethylene gasto the alkylation reactor 164.

Ethylene in the stream 126 reacts with the benzene in the alkylationreactor 164 to produce a combined product stream 172 that will includeethyl benzene, diethyl benzene (DEB), triethyl benzene (TEB) andunreacted ethane, ethylene and benzene.

The combined alkylation product stream 172 is passed to a benzene column174 where it is combined with a transalkylation product stream 176 fromthe transalkylation reactor 178. The transalkylation reactor 178converts the polyethyl benzenes (PEBs) such as DEB and TEB to EB and DEBrespectively. Hence, the feed for the transalkylation reactor 178 mayinclude a PEB stream 182 from the PEB column 180 coupled with benzenefrom the line 168 a taken from the feed line 168 to the alkylationreactor 164. The combined benzene/PEB stream 184 enters thetransalkylation reactor 178 after being heated by the boiler or heater186. The transalkylation product stream 176 will include lower amountsof PEBs.

The benzene column 174 removes benzene and lighter components throughthe overhead stream 188 which passes through condenser 190 and into thereceiver 192. Condensed benzene is recycled through the lines 168 and168 a to the alkylation reactor 164 and transalkylation reactor 178respectively. The vapor stream 194 from the condenser 192 is passed tothe lights removal column 196 where off gases are removed through theline 198 and cooling water is provided through the line 200. Heaviercomponents are drawn out the bottom of the column 196 through the line202 before passing into a collector 204 and through the line 206 to berecycled back to the receiver 192.

The bottoms stream 208 from the benzene column 174 contains ethylbenzene and heavier materials and is passed on to the ethyl benzenecolumn 210. The lighter ethyl benzene passes as overhead through theline 212, condenser 214, and a receiver 216 to the ethyl benzene productoutlet 218. The bottoms stream 220 from the ethyl benzene column 210 ispassed on to the PEB column 180 where PEBs are separated from heaviercomponents to produce a PEB product stream 220 and bottoms stream 222which is essentially a flux oil discharge stream. The PEB stream 220passes through the condenser 224 and receiver 226 before being recycledthrough the line 184 to the transalkylation reactor 178.

The intercoolers 63 a, 63 b in the alkylation section 164 typicallyrequire a cooling water utility. In accordance with this disclosure,integrating the alkylation intercoolers 63 a, 63 b (FIGS. 2-3) with theC₂− stripper 62 saves about 24 MM kcal/hr of additional heating by LPsteam which would be required by the reboiler 63 (FIG. 1). All of theheat for the reboiler 63 can be provided by the two intercoolers 63 a,63 b, each of which typically require about −16.5 MM kcal/hr for thecase described here. Additional cooling water duty will be required toremove the additional 9 MM kcal/hr of heat in the intercoolers 63 a, 63b, but overall the process is more efficient by reducing the steamrequirement for the stripper 62, as well as much of the cooling waterrequirement in the alkylation section 164.

Injecting the cold, liquid combined ethane/ethylene steam 136 provides adirect heat exchange benefit in the alkylation reactor 164. First, thehotter catalyst beds 165 b, 165 d and 165 f have a lower inlettemperature. This may result in better EB selectivity as some EBalkylation catalysts (such as UZM-8) have a slightly better EBselectivity at lower temperatures. Further, the lower inlet temperaturesto the alkylation reactor 164 provide reduced formation of heavies, suchas diphenyethane (DPE) and ethyldiphenylethane (EDPE). The outlettemperature of the hot catalyst beds 165 b, 165 d and 165 f is alsosomewhat lower. Therefore, the two intercoolers 63 a, 63 b have asmaller duty requirement, and even with the transfer of heat to thesplitter column 62, a savings results in terms of equipment cost(smaller heat exchanger area requirement), and utilities as coolingwater costs are reduced. A small portion of this advantage is offset bythe need to heat the recycle benzene in the line 168 to a slightlyhotter temperature in order to achieve the desired alkylation inlettemperature.

An overall summary of the disclosed process and integrated is shown infollowing tables with the date in the middle column being generatedusing a cool liquid combined ethane/ethylene stream and the data inright column using a conventional gaseous ethylene feed.

TABLE 1 Mixed C2 Polymer Grade C2 Feed Properties (Ethane/Ethylene)Ethylene (Prior Art) Ethylene Content (wt %)    87% 99.5% Temperature, °C.   12.2 89.5 Pressure (kPa) 4,520 4,520 Phase Liquid Gas EthyleneProcess Rate kg/hr 65,435  65,434

TABLE 2 Mixed C2 Polymer Grade Alkylation Chemistry (Ethane/Ethylene)Ethylene (Prior Art) Ethyl Benzene Selectivity 87.87% 87.69% DiethylBenzene Selectivity 11.34% 11.45% Triethyl Benzene Selectivity 0.70%0.75% Others 0.09% 0.11% Total 100.00% 100.00%

TABLE 3 Mixed C2 Polymer Grade Heavy Byproducts (Ethane/Ethylene)Ethylene (Prior Art) Diphenylethane 0.045% 0.052% Ethyldiphenylethane0.015% 0.018%

TABLE 4 Alkylation Reactor Inlet Temperatures (° C.) for Six Bed ReactorMixed C2 Polymer Grade (Ethane/Ethylene) Ethylene (Prior Art) Bed 1(Bottom; see bed 200.00 200.00 165a in FIG. 2) In Bed 1 Out 228.32228.40 Bed 2 In 222.24 227.13 Bed 2 Out 248.80 252.88 Bed 3 In 200.00200.00 Bed 3 Out 227.51 227.73 Bed 4 In 222.01 226.50 Bed 4 Out 247.38251.79 Bed 5 In 200.00 200.00 Bed 5 Out 226.69 227.06 Bed 6 (Top) In221.17 225.81 Bed 6 Out 246.02 250.79

TABLE 5 Alkylation Intercooler Duties (MM kcal/hr) Mixed C2 PolymerGrade (Ethane/Ethylene) Ethylene (Prior Art) Lower Intercooler (see−16.5 −19.4 intercooler 63b in FIG. 2) Upper Intercooler (see −16.5−19.4 intercooler 63a in FIG. 2) Total −33 −38.8

One additional integration option is illustrated in FIG. 3 and involveseliminating the transalkylation section 178 and the polyethyl benzenes(PEB) column 180. The ethyl benzene (EB) column bottoms 220 is passed tothe primary absorber 40 by combining the ethyl benzenes bottoms stream220 with the debutanized gasoline recycle stream 42 (FIG. 1) tosupplement some of the debutanized gasoline recycle, reducing the amountof recycle that is required. If all of the ethylene produced by the FCCprocess 10 a is used in the EB process 10 c, the EB column bottoms 220would reduce the required debutanized gasoline recycle stream 42 by anamount ranging from about 5 to about 10%. The polyethyl benzenesincluding DEB and PEB would ultimately end up as a high octane componentin the gasoline product stream 76. Because the EB column bottoms 220contains a small fraction of heavy components (e.g., diphenylethane,ethyldiphenylethane) that may be slightly too heavy for the gasolinepool, another alternative shown in FIG. 3 is to send the EB columnbottoms 220 to the FCC main column 22, where the heavier species in thisstream would be removed in a heavier fraction such as the heavy naphthadraw. The lighter species in this stream will still act to reduce therequired debutanized gasoline recycle stream 42, as they will exit inthe unstabilized gasoline stream 76 that is recovered from the maincolumn overhead stream 26.

Thus, improved processing schemes and arrangements are provided forobtaining ethylene and ethane via the catalytic cracking of a heavyhydrocarbon feedstock and converting the ethylene into ethyl benzenewithout separating the ethane from the feed stream. More particularly,processing schemes and arrangements are provided that advantageouslyeliminate any separation of ethylene from ethane produced by a FCCprocess prior to using the combined ethylene/ethane stream as a feed foran ethyl benzene process.

The disclosed processes and schemes may be practiced in the absence ofany element, part, step, component, or ingredient which is notspecifically disclosed herein.

1. An integrated system for catalytically cracking a hydrocarbonfeedstock, obtaining selected hydrocarbon fractions including a combinedethane/ethylene stream and reacting the ethylene of the combinedethane/ethylene stream with benzene to produce an ethyl benzene productstream, the integrated system comprising: a fluidized reactor zonewherein the hydrocarbon feedstock contacts a catalyst to produce acracked effluent stream including ethane and ethylene, a separation zonefor separating the cracked effluent stream into at least one separatorliquid stream and a separator vapor stream, the at least one separatorliquid stream comprising C₃+ hydrocarbons, the separator vapor streamcomprising ethane and ethylene; one or more treatment zones to removeimpurities from the separator vapor stream to provide a combinedethane/ethylene stream; a process line feeding the combinedethane/ethylene stream to an alkylation reactor of an alkylation zonefor reacting at least some of the ethylene in the combinedethane/ethylene stream with benzene to form ethyl benzene; a stripperfor stripping C₂− hydrocarbon materials from the separator liquid streamto form a C₃+ process stream substantially free of C₂− hydrocarbons; andat least one heat exchanger for transferring heat from the alkylationreactor to the stripper.
 2. The integrated system of claim 1 wherein thecombined ethane/ethylene stream is liquid and the process line furthercomprises a pump to pump the combined ethane/ethylene stream to thealkylation reactor.
 3. The integrated system of claim 1 wherein thealkylation zone comprises an ethyl benzene column to separate an ethylbenzene stream from a polyethyl benzenes stream, and wherein thepolyethyl benzenes stream is in communication with the absorption zonefor use as a solvent in an absorber.